Continous screen printing of organic light-emitting diodes

ABSTRACT

The invention relates to a device and method for continuous printing of organic light-emitting diodes (OLEDs). In this connection, a substrate with or without coating is provided as strip material on a roll, and is fed through a device with movable screens for imprinting by means of screen printing.

[0001] The invention relates to a device and method for continuous printing of organic light-emitting diodes (OLEDs).

[0002] Organic light-emitting diodes (OLEDs), based on organic material such as polymers and/or “small molecules” as the principal material of the functional layers, have developed very rapidly in recent years. Improved efficiency, a large number of new colors, and lower usage voltages make them of interest for many areas of application. Typical applications can be low-information-content passive-matrix displays with a few thousand pixels and an icon bar, backlights for LCDs, or planar illumination elements. The advantages of OLEDs, such as Lambert's reradiation and minimal thickness, are useful for these applications.

[0003] At present, the functional layers of which an OLED consists (e.g., poly(1,4-phenylene vinylene), PPV or polyfluorene, and/or derivatives of these materials) are usually applied to the glass or film substrate and/or to a bottom and/or structured layer using the spin-on application method. This method has a number of drawbacks: the bulk of the polymer solution (about 98%) is irretrievably lost, the spin-on application process is relatively lengthy (about 30-60 seconds) and, in the case of larger substrates, it is almost impossible to apply homogeneous functional layers.

[0004] For these reasons, alternative methods of applying organic material onto large surfaces are being sought. A number of printing processes are suitable for this purpose: screen printing, pad printing, inkjet printing, letterpress and rotogravure methods [e.g., D. A. Pardo, G. E. Jabbour, and N. Peyghambrian, “Application of Screen Printing in the Fabrication of Organic Light-Emitting Devices”; Adv. Mat., 2000, 17, p. 1249-1252; K. Mori et al., “Organic Light-Emitting Devices Patterned by Screen-Printing”; Jpn. J. Appl. Phys., 2000, 39, p. 942-944; Birnstock et al., “Screen-printed passive matrix displays based on light-emitting polymers”; Appl. Phys. Lett., Vol. 78, No. 24, 2001]. These printing methods are also advantageous because they permit the organic material to be applied after it has already been structured, making multichrome or full-color OLEDs possible.

[0005] Where a majority of the processes have thus far been developed for glass substrates, flexible substrates (e.g., films) will become increasingly important in the future.

[0006] The goal of the invention is to provide a device and method for the continuous application of soluble organic material, especially polymers, to substrate, especially flexible substrates, which operate continuously.

[0007] For economic reasons, the substrates should no longer be printed using a “stop-and-go” method, as is the case with classic printing on glass substrate, but instead should be coated in a continuous process using strip material, such as material “on a roll.” In this process, the film substrate, which may be pre-structured, is supplied on a roll and is imprinted with one or more polymers as the film is unwound from the roll in a uniform motion.

[0008] The invention solves the problem in that a special screen printing method is used to print the OLEDs.

[0009] The subject matter of the invention is a device for the continuous imprinting of a substrate-strip material by means of screen printing, comprising at least one printing screen and in which the substrate strip material is supplied on a roll, wherein a device for moving the printing screen is provided which ensures that it can accompany the strip material during printing and, following printing, be returned to its original position.

[0010] Another subject matter of the invention is a method for imprinting a substrate strip material by means of screen printing, in which the substrate is moved past at least one screen, wherein the screen accompanies the strip material during printing.

[0011] Finally, a subject matter of the invention is a product, such as an OLED, which comprises at least one functional layer that was applied in a continuous process by means of screen printing.

[0012] The term substrate strip material preferably describes flexible substrates such as films, etc., which exist in strip form. The substrate serves as the carrier of an OLED.

[0013] According to an advantageous embodiment, the device comprises a row of identically acting screens that are arranged in series and accompany successive areas of the strip material during printing. In particular, the row of screens consisting of an organic material and/or a screen stencil is arranged in such a way that there are no non-printed and therefore unusable areas on the strip material. Thus, virtually 100% of the strip is utilized and a section of the completely coated strip produces two edges of two substrates.

[0014] According to an embodiment, the device prints at a level of precision that typically permits a tolerance of only a few dozen μm.

[0015] According to an embodiment of the method, the substrate strip material is imprinted at a typical speed of 0.5 m/s, preferably in the range of 0.25 to 1 m/s.

[0016] Strip widths are preferably between 50 and 500 mm, depending on the application.

[0017] According to an advantageous embodiment of the device, several differently operating screens or rows of screens are arranged in series, so that a complete OLED can be produced in one device.

[0018] A substrate strip material is typically 0.005 to 1 mm thick and 50 to 500 mm wide.

[0019] It can also be advantageous that a certain distance between one imprinted area and the next on the substrate strip material is desired, so that a device without rows of screens, which has only one screen for each printing sub-step, is certainly preferable to a device with rows of screens, i.e., several identically operating screens for each printing sub-step. It can also be provided that, in a device with several screens, a row of screens can be used variably or parked, meaning that they are used or not used, depending on requirements. In addition to the screens with the template, a wiper blade and a tank for the solution of organic material, the device can also comprise a device for irradiating UV-curable functional layers, a heating system, a blower, a distributor and/or another apparatus for producing an OLED.

[0020] In one embodiment, a cutting and/or stamping device for separating and/or encapsulating the individual OLEDs is provided at the output of the device, where the fully printed strip material exits the device.

[0021] Other elements, such as the device for unwinding the substrate-strip material as well as for maintaining the necessary strip tension area also comprised by the device and are part of the state of the art, which is the reason they are not described in great detail.

[0022] The imprinting of a uniformly moving film is not trivial, because the classic “roll-on-roll” processes (offset printing, etc.) cannot be used. This is because the photosensitive resist structures already located on the film are critical in this regard. As a result of these contact methods, they are either destroyed or transfer of the polymer solution is prevented. The conventional “stop and go” procedure unnecessarily stresses the substrate film during printing, which is not the case with the continuous method.

[0023] Another advantage of the process is the high speed and great precision with which the OLEDs can be produced.

[0024] In the following, the invention is described in greater detail on the basis of an exemplary embodiment:

[0025] The production of a flexible, monochromatic display based on organic light-emitting diodes using the special “screen-on-roll” screen printing method:

[0026] A transparent film impermeable to water and oxygen is structured with ITO (indium tin oxide) and provided with photoresist structures. (The purpose of the photosensitive resist structures is to separate the individual cathode strips and confine the printed polymer surfaces. These processes are known and well-understood.) As a result of the pre-structuring of the film, hundreds of individual passive-matrix displays are defined. The film is provided wrapped on a roll. Using the special screen printing machine, several conjugated polymers are consecutively printed onto the film and dried using suitable means. In this printing process, the film can be moved through the machine in a uniform motion. Finally, a cathode is vapor deposited in a structured manner (e.g., through shadow masks) and the active side of the film is also sealed to be watertight and airtight. Now the individual displays can be cut out and contacted.

[0027] The invention relates to a device and method for continuous printing of organic light-emitting diodes (OLEDs). In this connection, a substrate with or without coating is provided as strip material on a roll, and is fed through a device with movable screens for imprinting by means of screen printing. 

1-9. (Canceled).
 10. A device for continuous imprinting of a substrate strip material that is supplied on a roll, comprising: a first printing screen; and a printing screen moving device to cause the first printing screen to move from a first position while accompanying the substrate strip material as the substrate strip material is unwound from the roll and to return to the first position.
 11. The device of claim 10, further comprising: a row of printing screens including the first printing screen.
 12. The device of claim 11, wherein: the printing screens in the row of printing screens operate identically.
 13. the device of claim 11, wherein: at least two printing screens in the row of printing screens operate differently from each other.
 14. The device of claim 10, wherein: the first printing screen includes an organic material.
 15. The device of claim 10, further comprising: a second printing screen positioned in series with the first printing screen.
 16. The device of claim 10, further comprising at least one of a UV irradiation device for irradiating UV-curable functional layers, a heating system, a blower and a distributor.
 17. The device of claim 10, further comprising: a cutting device for separating the substrate strip into individual organic light emitting diodes.
 18. The device of claim 10, further comprising: a stamping device for encapsulating individual organic light emitting diodes.
 19. The device of claim 10, wherein: the printing screen moving device moves the printing screen at a speed of about 0.25 m/s to about 1 m/s.
 20. The device of claim 10, wherein: the printing screen moving device moves the printing screen at a speed of about 0.5 m/s.
 21. The device of claim 10, further comprising: a wiper blade for forcing organic material through the first printing screen; and a tank for providing a solution of the organic material.
 22. A method of screen printing on a substrate strip material, comprising: moving a substrate strip from a roll through a device having a printing screen; moving the printing screen with the substrate; and printing onto the substrate using the printing screen as the screen moves with the substrate.
 23. The method of claim 22, wherein: moving the printing screen includes moving the screen between a speed of about 0.25 m/s to about 1 m/s.
 24. The method of claim 22, wherein: moving the printing screen includes moving the screen at a speed of about 0.5 m/s.
 25. The method of claim 22, further comprising: irradiating a UV-curable functional layer.
 26. The method of claim 22, further comprising: cutting a printed substrate strip to separate individual organic light emitting diodes.
 27. The method of claim 22, further comprising: encapsulating a printed substrate strip to encapsulate individual organic light emitting diodes.
 28. A method of forming a organic light emitting diode, comprising: unwinding a substrate from a roll through a device having a plurality of printing screens; printing a conjugated polymer onto the substrate using the plurality of printing screens as the substrate moves through the device to form a printed substrate strip; moving the printing screen with the substrate; depositing a cathode onto the printed substrate strip; encapsulating the printed substrate strip to encapsulate individual organic light emitting diodes; and cutting the printed substrate strip to separate the individual organic light emitting diodes. 